fix: harden first-run install and clean reinstall

oa-backend/build.gradle

@@ -8,6 +8,8 @@ group = 'com.kaidi'
 version = providers.gradleProperty('releaseVersion')
         .orElse(System.getenv('ERP_RELEASE_VERSION') ?: '0.1.0')
         .get()
+def flywayVersion = '11.20.3'
+def postgresqlDriverVersion = '42.7.13'
 def productionBuild = providers.gradleProperty('productionBuild')
         .map { it.toBoolean() }
         .orElse(false)
@@ -47,9 +49,9 @@ dependencies {
     implementation 'org.springframework.boot:spring-boot-starter-websocket'
 
     // Production database and versioned schema migrations.
-    implementation 'org.flywaydb:flyway-core:10.22.0'
-    runtimeOnly 'org.flywaydb:flyway-database-postgresql:10.22.0'
-    runtimeOnly 'org.postgresql:postgresql'
+    implementation "org.flywaydb:flyway-core:$flywayVersion"
+    runtimeOnly "org.flywaydb:flyway-database-postgresql:$flywayVersion"
+    runtimeOnly "org.postgresql:postgresql:$postgresqlDriverVersion"
 
     // SQLite remains available to source-tree development and tests, but is
     // deliberately absent from PostgreSQL-only production release artifacts.
@@ -69,9 +71,9 @@ dependencies {
 
     installerImplementation 'org.springframework.boot:spring-boot-starter-web'
     installerImplementation 'org.springframework.boot:spring-boot-starter-validation'
-    installerImplementation 'org.flywaydb:flyway-core:10.22.0'
-    installerRuntimeOnly 'org.flywaydb:flyway-database-postgresql:10.22.0'
-    installerRuntimeOnly 'org.postgresql:postgresql'
+    installerImplementation "org.flywaydb:flyway-core:$flywayVersion"
+    installerRuntimeOnly "org.flywaydb:flyway-database-postgresql:$flywayVersion"
+    installerRuntimeOnly "org.postgresql:postgresql:$postgresqlDriverVersion"
 }
 
 tasks.named('test') {